Clojure

It is time for another update.

I am done for the time being editing and making changes to my site. For now I will stick with WordPress, and I will leave the old posts intact.

I have been working more with Clojure. I have not done a lot with Programming Clojure, and at some point I plan on finishing it. I need to work on learning more about Clojure and its capabilities, but I think I want to make an app, even a small one. I think it can help some of the information stick more, and after a while just doing tutorials is a slog. Granted, maybe if I kept going for a few more pages, I would read about something that would give me an idea, but for now I will look into other things. I have mentioned this in the past, but I would like to get into the Clojure rules engine Clara. (Granted, there are a lot of things I would like to do.)

I have been looking into web frameworks for Clojure. I started looking into Luminus more. I went through the first few pages of the tutorial a few years ago, but recently when I tried to run the application it did not work. So I started over. There have been a few changes. My goal was to be able to add some code to get the same results as the Rails routes for a database table. I know a lot of people like to make REST apps, but from what I have seen, when people make REST apps they add data by sending JSON requests and typing them by hand. I find this to be tedious. I went through a tutorial on Pluralsight on making web services with Go, and typing requests in Postman was a drag. This was a few years ago, and I looked at Postman again more recently for work. There were limits on what you could do with the free version. Maybe making forms on HTML pages is more work, but I was put off by Postman.

So I started going through the Luminus tutorial and taking more thorough notes. I went to the Luminus channel on the Clojurians Slack, and someone made a reference to a new framework named Kit. The developer behind Luminus (who goes by “Yogthos” online) is one of the Kit developers. I get the feeling that Kit is intended to replace Luminus. Judging by the projects’ commit histories, Yogthos seems to be spending more time on Kit than Luminus lately. He has a post on his website about Kit; he never comes out and says that Kit is replacing Luminus, but that seems to be the takeaway. Another one of the Kit developers has a post on his site here.

Also, Kit uses the Clojure CLI tools. Luminus uses Leiningen, and gives you the option to use Boot as well (which I think is a hint that Luminus will get less attention going forward than Kit). The CLI tools seemed to have killed Boot stone dead. The most recent tag in the Boot repo was on 2019-04-13. (Granted, Luminus’s most recent tag was in 2015.) I have been seeing fewer mentions of Boot since the CLI tools came out. I think CLI really took away a lot of Boot’s momentum. I am getting the feeling that CLI is also taking some mindshare from Leiningen, although this is happening more slowly since Boot was not as popular as Leiningen. It looks like CLI tools are the future.

So I have also spent some time with the CLI tools. There is a site with some Clojure tutorials called Practicalli. They have a nice page on the CLI tools and a repo with a nice deps.edn config file. For the most part it is pretty easy, but it is a drag learning something else. I am not sure I have got the hang of using CIDER with the CLI tools. I had to run the app in one terminal, and fire up Emacs in another to use CIDER. With Leiningen, I could do it all in Emacs.

Another difference is Luminus manages state with Mount, while Kit uses Integrant. I need to spend some time studying Integrant.

I then “pivoted” to Coast, a web framework that tries to be the Rails for Clojure (site here, Github repo here). It has been around for a few years. I did not look at it because it uses the CLI tools, and for a long time I was not interested in learning about CLI tools. Coast also uses make, which strikes me as odd. Right now I am intersted in making a web app in order to quickly work with data, so I thought that since I am looking into CLI tools, why not try Coast. Plus it looks like Kit is still a work in progress (the devs pretty much said that on Slack), so I will let it percolate for a while. Interesting note: I think Yogthos starting working on Kit not too long after the third edition of his book came out.

Coast uses Make for some tasks. That is make, or as cats on the internet would put it: The thing that runz ur see code. Although if you look at the Makefile, the Make commands are aliases to clj commands. So if you really wanted to stick with pure Clojure, you could just run the clj commands.

Recently there was a post on Hacker News about a new web framework for Go called Bud (Hacker News post here, Github repo here). One of the commenters told the Bud developer to try to avoid the word “framework” because a lot of people in the Go community hate the concept, even though some commenters thought that frameworks are useful. When I was in The Starter League, one of the instructors said he liked to handle sessions and authentication himself. I never understood this mentality. A lot of web apps are going to have common needs: handling sessions, routes, authentication, authorization, database connections. What you usually care about is what comes after. I would like to make some pages so I can create data so I can look into a rules engine.

I think you are more likely to make changes to an existing app than build one from scratch. So score one for the framework crowd. Plus, whether the anti-framework people like it or not, this question will come up until there is an answer. I bet nobody looks at Ruby and asks how to write a web app in Ruby.

You’re welcome.

Image from an 11th century manuscript known as Dionysiou 587, created and housed at the Monastery Agios Dionisiou on Mount Athos, assumed allowed under Public Domain.

I got done with chapter 4 of Programming Clojure. This chapter was about functional programming.

Interestingly, they did not spend much time in this chapter on the concept of higher-order functions. They did use them, but it was not a major part of their definition of “functional programming”. They talked more about purity, referential transparency, immutability, persistent data structures, recursion, and laziness and eagerness (for both collections/sequences and transformations).

I have noticed that when Lisp/Scheme programmers talk about “functional programming”, they tend to talk about functions: higher-order, purity, immutability, laziness. When Haskell or Scala programmers talk about “functional programming”, they talk about types as much as they talk about functions.

The section on lazy sequences blew my mind. They worked with Fibonacci numbers, and I made a lazy sequence of factorials. It is amazing that you can calculate some very large numbers very quickly without blowing the stack.

In case you were wondering, here is 200 factorial (split across a few lines so there is no horizontal scroll):

788657867364790503552363213932185062295135977687173263294742533
244359449963403342920304284011984623904177212138919638830257642
790242637105061926624952829931113462857270763317237396988943922
445621451664240254033291864131227428294853277524242407573903240
321257405579568660226031904170324062351700858796178922222789623
703897374720000000000000000000000000000000000000000000000000N

That’s 7.88657 times 10 to the 374th. My answer matches what is on Calculator Soup.

Here is my sequence:

(defn lazy-seq-fact
  ([]
   (concat [1N 1N 2N] (lazy-seq-fact 3N 2N)))
  ([a b]                                                                                                     
   (let [n (* a b)]
     (lazy-seq (cons n (lazy-seq-fact (inc a) n))))))

(nth (lazy-seq-fact) 200)

I am not quite sure I understand transducers or eduction as well as I would like. (I think they may be changing the meanings of the words “eduction” and “transducer” slightly.) I think one of the ideas behind transducers is that a transducer can be more efficient and do things in fewer steps. A threading macro with multiple functions will make a sequence or collection at each step. A transducer does not. They had a couple of examples that they converted from using the threading macro to using transducers and “into”. Only the first step in ->> (the starting collection, where it comes from) and the last step in ->> (the final collection, where to put it, which was a call to “vec”) are flipped when we go to “into”; the transformation steps are pretty much the same. In their example, they combined the steps into a function with “comp”. Also: transducers go right-to-left, which is unintuitive for me.

I think you use “eduction” when you want to transduce part of a collection and not have dangling resources.

I did not understand the threading macro until I had a need for it. Perhaps transducers and eduction will be the same.

I did find a way to use the partition function to work with moving averages. You need the members of your collection to be in order from most recent to oldest. The you can get a collection of moving averages with this:

(map #(/ (reduce + %1) 
         (count %1)) 
     (partition 4 
                1 
                coll-most-recent-to-oldest))

Chapter 5 is about spec. Clojure seems to have a lot of concepts that are new to me, even more than the little Scheme I have worked with.

You’re welcome.

Image from the Liuthar Gospels, a tenth century manuscript created in southern Germany, currently housed in the cathedral of Aachen, assumed allowed under public domain. I have read there are 30 full-page miniatures in the manuscript, but I have not been able to find a pdf or any other pictures than the one on this page.

I am still going through Purely Functional. It is interesting that there are so many ways to define a function in Clojure. I wonder if all functional languages are like that.

I have decided to spend time looking into making web apps in Clojure. I know that AI is big, and it would be nice for Clojure to be a force in that space, but things seem to have changed since I blogged about it in May.

The guy who wrote Guildsman is no longer updating it. I don’t know what is going on with dl4clj. (Granted, I haven’t emailed the guy.) The Deeplearning4J site said that was the official Clojure library for Deeplearning4J. It looks like they are now part of the Eclipse Project, and they totally redid their site. And in my opinion, not very well. There are lots of things that look like links on their FAQ page, but nothing happens when you click them. They have a gitter chat. I will try looking into that sometime. The search on gitter is not that great. I think you have to go day-by-day. Here is the link for the archive on 2018-09-26. Cortex still looks like it is or will be a ghost town. If only someone could make all this stuff less complicated.

I will get more into web apps. I know a lot of people think that mobile is the future, but I think web apps will be around for a while. When the iPad came out in 2010, all the Apple fanboys said that within five years we would all be using iPads for everything all the time. But that did not happen. At my job, we all use laptops. When I go to tech meetups, people still use laptops. Gamers are still into desktops.

Sidenote: One thing that I find odd and frustrating is that while 15-20 years ago a lot of technology people thought they were so smart and sophisticated for not trusting Microsoft (or IBM, or Oracle), yet ever since the iPhone came out, those same people won’t say the sun is out until Apple says so. Yet tech people used to make fun of the suits for not thinking the sun is out unless MS said so. Was I wrong to believe in open source?

For one thing, web browsers are on more devices. Phones, tablets and laptops/desktops can all use web apps, but laptops and desktops cannot use mobile apps. Plus I have a hard time typing on phones, and dealing with passwords on phones is very frustrating for me. I prefer dealing with passwords in a password manager or a spreadsheet or an encrypted file. I prefer keeping track of logins and passwords that way rather than deal with a bunch of apps on a phone.

And EVERYBODY makes an app. My bank. My insurance company. The company that processes my rent payments. Which I could make using the app from my credit card company. There is an app for all those stupid scooters all over Austin. Every mom-and-pop Indian place here has an app. My gym has an app. Everybody that Robert Llewellyn talks to on “Fully Charged” has an app. I know my phone is old, but I don’t have a lot of space. I would rather use that space for pictures than yet another app that I might only use one time.

Laptops have bigger screens, bigger keyboards, more hard drive space, more memory; since when did Americans want less?

So there was a thread on the Clojure Google group recently about web apps. A lot of libraries were mentioned. I will go with Luminus first. He walks you through what libraries you need, and you can pick and choose which ones you want to use. Others that were mentioned: Pedestal, Yada, Integrant, and Duct.

I know a lot of Clojure people (and Lispers in general; should we call them Lispters?) don’t like frameworks. They prefer libraries. I never liked the answer “go use libraries.” Nobody ever tells you what libraries to use. I think a lot of people want to be able to produce something quickly that they can see, and frameworks do that. People always like to contrast the “stringing together libraries” approach with Rails. I think that while something like Rails has a lot of “magic” and can do a lot of things for you, magic was not the only reason Rails took off.

What I think helped Rails is that it gave people a default answer. Back then, there was PHP: not a language anybody really loves, and you have to do everything yourself every damn time. “How do you make an app in PHP? From the ground up. Every stinking time.” And you have Java: Lots of frameworks, some of them viable and widely used, some niche. How do you know you are making a good choice and your framework won’t be abandoned later? “How do I make a web app in Java? Pick a framework. We got plenty: A, B, C, D, etc, etc. And then pick a servlet engine. We got a lot of those too!”

“How do I make a web app with Ruby? Use Rails. Go here and do this.” The shortest and most useful answer. Granted, there are/were other frameworks in Ruby, so if you don’t like Rails you have options. But I think having a default answer is the way to go. Choice is great when you understand the choices.

Some people want to make an app, and then go under the hood.

You’re welcome.

Image from ‘Moralia in Job’, a 10th century manuscript at the National Library of Spain, licensed under CC BY-NC-SA 4.0.

I am putting twitter-retriever-gradle on hold. I spent a couple of hours trying to send JVM system properties to the clojureRun task, and I couldn’t figure it out.

I raised an issue on the github repo for the Clojure Gradle plug-in. They made a suggestion, and it did not work out. I was using a few libraries that could use system properties for configuration. That is not the only way to do things, but with Gradle my other option was to have multiple copies of the same file all over the repo. I would rather not do that.

I might ask on the Gradle forum. But for now, I think I will move on to something else.

I think Gradle works well for Groovy and Java. It seems a bit harder to use for Clojure. Back to Purely Functional.

You’re welcome.

Image from ‘Biblia de Ávila [Manuscrito] : [Vetus et Novum Testamentum cum praefationibus et argumentis Sancti Iheronymi et aliorum]’, an 11th century manuscript at the National Library of Spain, licensed under CC BY-NC-SA 4.0.